While memory effects have been reported for dense enough disordered systems
such as glasses, we show here by a combination of analytical and simulation
techniques that they are also intrinsic to the dynamics of dilute granular
gases. By means of a certain driving protocol, we prepare the gas in a state
where the granular temperature T coincides with its long time limit. However,
T does not subsequently remain constant, but exhibits a non-monotonic
evolution before reaching its non-equilibrium steady value. The corresponding
so-called Kovacs hump displays a normal behavior for weak dissipation (as
observed in molecular systems), but is reversed under strong dissipation, where
it thus becomes anomalous.Comment: 5 pages, to appear in Physical Review Letter
